Which of the following opposes the flow of blood back to the heart?
A) vascular resistance
B) peripheral veins have valves to prevent backflow of blood
C) muscular pumps squeeze veins and move blood toward the heart
D) blood pressure
E) blood pressure gradient from arteries to veins
Question 2
The average length of the menstrual cycle is ________ days.
A) 16
B) 19
C) 21
D) 28
E) 35